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Message-ID: <49B4A704.7030309@sbcglobal.net>
Date: Mon, 09 Mar 2009 01:20:04 -0400
From: John Slade <sladerj@sbcglobal.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Ground Testing
References: <list-3533625@logan.com>
In-Reply-To: <list-3533625@logan.com>
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Welcome, Jim.
You will get differing answers to that question. Mine is "not much 
beyond the integrity of the engine itself".

Installation of a rotary in a Cozy is fairly tight and, by the way, in 
my opinion a 20b is a little too big, long and heavy. Apart from test 
running the engine to be sure that it's been correctly rebuilt, most of 
what you do on a test stand will be a waste of time and effort. When 
installed on the plane the engine is dependent on many systems that 
either can't be effectively duplicated on a test stand, or will have to 
be re-engineered when installed in the plane.  Sure, if you can get your 
hands on a dyno you can test power and tune, but once you put the engine 
on the plane you'll have to wire the engine into the plane's systems and 
implement fuel, ignition, injection, cooling and exhaust systems that 
fit in the cowl. Testing those systems in the "real world" is really 
only possible with air flowing through (and over) the cowl into a prop 
at 200 mph and at various attitudes.

A normally aspired Renesis will work well, but I think will need very 
careful attention to intake and exhaust optimization to get the power 
you're probably hoping for. Next you will need some sort of muffler that 
can hold up. I wasn't keen on hanging a muffler below the fuselage like 
the RV guys do. There isn't much room for that in a Cozy and it would 
look very ugly and draggy. Putting a red hot muffler inside the cowl is 
a heat radiation problem, plus there's very little room. A turbo is 
relatively small, circular and easily screened for heat. My approach was 
that the easiest way to silence the roar was to install a turbo. This 
way you don't have to bother with an exhaust system, and the intake 
system is much less critical. This gives added (and exciting) benefits 
in take-off and cruise power, but comes with its own complexity. The 
trick seems to be to use the right turbo. Then, if you use a turbo, the 
Renesis is a little high in compression ratio and you might be better 
with a 3rd generation 13B. I'm working with another builder right now on 
his Cozy project. We are duplicating my 13B exactly. That might be a 
useful indication of whether I consider it a success. The Cozy Girrrls 
are very knowledgeable on this rotary stuff,  and they also are 
installing a 3rd gen 13B with a big turbo.

In general, I'd say the rotary is more risky to start with - say the 
first 50 hours - because every installation is different and errors WILL 
occur. After the first 50 hours I think the rotary is well worth it. 
It's safer, faster, quieter, very much smoother, and much cheaper to 
maintain. The devil is in the peripherals. Redundancy is key. I have 
redundant fuel tanks, filters, pumps, injectors, plugs, ignition 
computers, batteries. Failure of any item is survivable because I have a 
spare. The problem is that redundancy breeds complexity - this is where 
the extra build and testing time comes from. I'd recommend the IVO 
in-flight adjustable prop.

I've seen too many failed rebuilds by people who have much more 
experience and talent than I, to risk applying my skills to this most 
critical part. Also, there's enough to do with the peripherals and I 
didn't need the learning curve. Unless you're determined to rebuild your 
own you might consider using an expert who's done it 1000 times and 
knows what to modify for aviation build your engine. Given your 
investment in the plane, a professionally rebuilt engine is cheap 
insurance. Instead, I'd suggest concentrating your effort on getting the 
peripherals perfect, adding redundancy everywhere you can get it.

Having said all this, my take, for what its worth, would be to forget 
the engine for a while and spend every spare waking moment building 
yourself an airframe. Given that you have a few years to make the engine 
decision, use those years to see what happens with other installations.

I hope this helps in your decision process, or at least starts yet 
another heated discussion you can learn from :).
Regards,
John Slade
Turbo Rotary Cozy, N96PM.
98 hours and purring like a kitten.